Vegetation variables and rhizosphere bacterial communities from ten paired sites in southwestern Finland, 2021

Plant invasions can have major impacts on ecosystems not only in
aboveground but also in belowground through changes in microbiota.
Particularly legumes, which often host nitrogen-fixing symbionts
(rhizobia), can be expected to modify soil bacterial communities. We
examined the effect of the invasive herbaceous legume, Lupinus
polyphyllus, on the alpha diversity and community composition of soil
bacteria. We also explored whether vegetation cover, the cover of other
(non-invasive) legumes or number of vascular plants was associated with
soil bacterial communities. We sampled rhizosphere soil and surveyed
vegetation from ten paired sites (invaded more than ten years ago and
uninvaded locations) in southwestern Finland, and identified bacterial DNA
by using 16S rRNA gene amplicon sequencing. The plant invader and the
three vegetation variables considered had no effect on soil bacterial
alpha diversity in terms of bacterial richness, Shannon and Inverse
Simpson diversity indices. The composition of soil bacterial communities
differed between invaded and uninvaded soils at four out of the ten sites.
However, the differences in the relative abundances of top bacterial
families between the two soil origins were inconsistent across sites,
including rhizobia in the family of Bradyrhizobiaceae that the study
species is hosting. Moreover, vegetation cover, legume cover after
excluding the study species, and number of plant species explained a small
proportion of the variation in the bacterial community composition. Our
findings indicate that L. polyphyllus has the potential to modify the soil
bacterial community composition locally, at least at sites where it has
been present for more than a decade.